5-year study finds SMA treatment leads to motor function gains

Treatment with Spinraza (nusinersen) led to sustained improvements in motor function in children and adolescents with spinal muscular atrophy (SMA), according to a real-world study from Czechia and Slovakia.

Improvements were generally greatest during the first months of therapy and more pronounced in younger children, with benefits largely maintained over five years. However, some patients experienced worsening mobility, breathing difficulties, and scoliosis (abnormal spine curvature) despite treatment.

“Our long-term data showed that [Spinraza] improved motor functions and this improvement was mostly maintained during the 5-year follow-up,” the researchers wrote.

The study, “A multicenter, prospective – retrospective, epidemiological study in Czech and Slovak minors with spinal muscular atrophy treated with nusinersen,” was published in the Journal of Rare Diseases.

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SMA is marked by the progressive loss of motor neurons, the nerve cells that control movement, leading to muscle weakness and wasting. SMA is caused in most cases by mutations in the SMN1 gene that result in insufficient production of the SMN protein, which is essential for motor neuron health.

Spinraza, marketed by Biogen, works by helping the SMN2 gene, a sort of backup gene, to make more functional SMN. Administered by injection into the fluid surrounding the spinal cord, it is designed to preserve motor neurons and improve or maintain motor abilities.

To assess Spinraza’s long-term effects in routine clinical practice, researchers analyzed data from 153 patients who started treatment before age 19. Participants were included in REaDY, a registry of people with neuromuscular diseases in Czechia and Slovakia.

Most participants began showing symptoms shortly after birth. The median age at Spinraza initiation was 3.3. Most patients had SMA type 1 (37.3%) or type 2 (37.9%), while 23.5% had SMA type 3. Two participants started treatment before developing symptoms.

During the five-year follow-up, motor function generally improved for the 141 participants with available assessments at the time of treatment initiation (baseline). Scores on two standard motor function tests, CHOP-INTEND and Hammersmith Functional Motor Scale – Expanded, significantly improved during the first two years, and remained better than before treatment through five years.

The greatest functional gains were in the ability to sit without support and to roll onto the side, although some patients lost motor skills, particularly the ability to stand and to walk independently.

Arm and hand function, assessed using the Revised Upper Limb Module, improved during the first years of treatment, followed by worsening and stabilization thereafter.  Walking endurance improved during the first two years, but returned to pretreatment values after three and four years, and worsened after five years.

Patients who could control their heads, roll, sit independently, or climb stairs before treatment maintained these abilities later on, as did most of those who were initially able to stand or walk independently.

Children younger than 6 generally experienced greater improvements than older patients.

“In motor scales, the strongest therapeutic effect was observed during the first six months; in children up to six years of age, the improvement continued for 24–36 months,” the researchers wrote.

Despite motor improvements, scoliosis became more common during follow-up, with 27 patients newly documented at their final assessment.

The researchers suggest that physical growth, weight gain, and complications such as scoliosis and contractures — tightening of muscles and tissues that restrict movement — may contribute to worsening mobility despite treatment. “The risk of scoliosis development was high, which points out the importance of prevention,” they wrote.

Most patients maintained the ability to feed themselves, but eight experienced worsening feeding function. Seven began requiring noninvasive breathing support, while one required invasive ventilation. The researchers said this indicates that some patients experienced the expected progression of SMA-related complications affecting swallowing and breathing.

Spinraza was generally well tolerated. The most common side effects were headache, back pain, and vomiting, but these gradually decreased over time.

At the study’s cutoff date, 140 of the original 153 patients (91.5%) were alive, seven were lost to follow-up, and six had died, mostly from respiratory complications. Sixty-nine patients switched to other disease-modifying therapies during follow-up.

“We conclude that in the paediatric population, [Spinraza] therapy generally resulted in improvement of their condition,” the researchers wrote.